We have continued work on the high resolution structure of the bifunctional enzyme complex tryptophan synthase. We have examined mutants in order to understand the mechanism of action of both enzymes and the mechanism of communication between the two active sties. The native enzyme structure has been refined to 1.9A resolution. A sodium binding site has been confirmed by the examination of enzyme in the presence of K+ and Cs ions. Changing the cation produced unexpected changes in the structure that can be related to the allosteric properties of the enzyme and the channeling of the indole intermediate between the active sites. Domain III of pseudomonas Aeruginosa exotoxin has been crystallized and the structure determined. The enzyme was crystallized with NAD which undergoes slow hydrolysis to give AMP and nicotinamide. We have now been able to bind a nonhydrolysable analog of NAD that permits us to see the NAD binding site. The 30kD N-terminal domain of enzyme 1 of (PTS), the phosphoenolpyruvate: sugarphosphotransferase system has been crystallized and the three- dimensional structure determined.